Abstract

DNA was extracted from water and sediment samples taken from acidic, geothermal pools on the Caribbean island of Montserrat. 16S rRNA genes were amplified by PCR, cloned, sequenced, and examined to indicate some of the organisms that might be significant components of the in situ microbiota. A clone bank representing the lowest temperature pool that was sampled (33 degreesC) was dominated by genes corresponding to two types of acidophiles: Acidiphilium-like mesophilic heterotrophs and thermotolerant Acidithiobacillus caldus. Three clone types with origins in low- and moderate- (48 degreesC) temperature pools corresponded to bacteria that could be involved in metabolism of sulfur compounds: the aerobic A. caldus and putative anaerobic, moderately thermophilic, sulfur-reducing bacteria (from an undescribed genus and from the Desulfurella group). A higher-temperature sample indicated the presence of a Ferroplasma-like organism, distinct from the other strains of these recently recognized acidophilic, iron-oxidizing members of the Euryarchaeota. Acidophilic Archaea from undescribed genera related to Sulfolobus and Acidianus were predicted to dominate the indigenous acidophilic archaeal population at the highest temperatures.